Old Contax cameras have a metal ring on the rangefinder window that some users report can damage eyeglasses.

This bumper threads onto that ring and is less likely than the metal is to scratch eyeglasses. The bumper is not threaded. The PETG that I used is soft enough that the threaded ring forms its own threads in the plastic part. A wrench is also provided for installation / removal if needed.

Probably a darker colour would be better than the brown that I used.